The “strength” or “weakness” of doughs are an important aspect of making farinaceous finished products from doughs, including baking. The “strength” or “weakness” of a dough is primarily determined by its content of protein and in particular the content and quality of the gluten protein is an important factor in that respect. Flours with a low protein content are generally characterized as “weak.” Thus, the cohesive, extensible, rubbery mass which is formed by mixing water and weak flour will usually be highly extensible when subjected to stress, but it will not return to its original dimensions when the stress is removed.
Flours with a high protein content are generally characterized as “strong” flours and the mass formed by mixing such a flour and water will be less extensible than the mass formed from a weak flour, and stress which is applied during mixing will be restored without breakdown to a greater extent than is the case with a dough mass formed from a weak flour. Strong flour is generally preferred in most baking contexts because of the superior rheological and handling properties of the dough and the superior form and texture qualities of the finished baked or dried products made from the strong flour dough.
Doughs made from strong flours are generally more stable. Stability of a dough is one of the most important characteristics of flour doughs. Within the bakery and milling industries it is known to use dough “conditioners” to strengthen the dough to increase its stability and strength. Such dough conditioners are normally non-specific oxidizing agents such as e.g. iodates, peroxides, ascorbic acid, K-bromate or azodicarbonamide and they are added to dough with the aims of improving the baking performance of flour to achieve a dough with improved stretchability and thus having a desirable strength and stability. The mechanism behind this effect of oxidizing agents is that the flour proteins, in particular gluten contains thiol groups which, when they become oxidized, form disulphide bonds whereby the protein forms a more stable matrix resulting in a better dough quality and improvements of the volume and crumb structure of the baked products.
However, the use of several of the currently available non-specific oxidizing agents is either objected to by consumers or is not permitted by regulatory bodies. Hence it has been attempted to find alternatives to these conventional flour and dough additives, and the prior art has i.a. suggested the use of glucose oxidase and hexose oxidase for this purpose.
Glycerol oxidase is an oxidoreductase which is capable of oxidizing glycerol. Different types of glycerol oxidase have been described in the literature. Some of these glycerol oxidases need co-factors in order to oxidize glycerol (Shuen-Fu et al., 1996. Enzyme Micro. Technol., 18:383-387).
However, glycerol oxidase from Aspergillus japonicus does not require any co-factors in the oxidation of glycerol to glyceraldehyde (T. Uwajima and O. Terada, 1980. Agri. Biol. Chem. 44:2039-2045).
This glycerol oxidase has been characterized by T. Uwajima and O. Terada (Methods in Enzymology, 1982, 89:243-248) and T. Uwajima et al. (Agric. Biol. Chem., 1979, 43:2633-2634), and has a pH optimum at 7.0 and Km and Vmax are 10.4 mM and 935.6 μmol H2O2 min−1 respectively using glycerol as substrate. The enzyme is most active on glycerol but also other substrates like dihydroxyacetone, 1,3-propanediol, D-galactose ad D-fructose are oxidized by glycerol oxidase.
Glycerol oxidase not requiring co-factors has also been isolated from Penicillium and characterized by Shuen-Fuh Lin et al. (Enzyme Micro. Technol., 1996, 18:383-387). This enzyme has optimum activity in the pH range from 5.5 to 6.5 at 30° C. The enzyme is stable between 20 and 40° C. but loses its activity at temperatures above 50° C.
Other potential sources for glycerol oxidase according to the invention include different fungal species as disclosed in DE-2817087-A, such as Aspergillus oryzae, Aspergillus parasiticus, Aspergillus flavus, Neurospora crassa, Neurospora sitophila, Neurospora tetrasperma, Penicillium nigricans, Penicillium funiculosum and Penicillium janthinellum. 
Glycerol oxidase isolated from the above natural sources has been used for different applications. Thus, glycerol oxidase from Aspergillus japonicus has been used for glycoaldehyde production from ethylene glycol (Kimiyasu Isobe and Hiroshi Nishise, 1995, Journal of Molecular Catalysis B: Enzymatic, 1:37-43). Glycerol oxidase has also been used in the combination with lipoprotein lipase for the determination of contaminated yolk in egg white (Yioshinori Mie, 1996. Food Research International, 29:81-84). DE-2817087-A and U.S. Pat. No. 4,399,218 disclose the use of glycerol oxidase for the determination of glycerol.
It has now been found that the addition of a glycerol oxidase to a flour dough results in an increased resistance hereof to deformation when the dough is stretched, i.e. this enzyme confers to the dough an increased strength whereby the dough becomes less prone to mechanical deformation. Accordingly, glycerol oxidase is highly useful as a dough conditioning agent in the manufacturing of flour dough based products including not only bread products but also other products made from flour doughs such as noodles and alimentary paste products.
It has also been found that the dough strengthening effect of glycerol oxidase is potentiated significantly when it is combined with a lipase, which in itself does not affect the dough strength. Furthermore, the combined use of glycerol oxidase and lipase results in an improvement of bread quality, in particular in respect of specific volume and crumb homogeneity, which is not a simple additive effect, but reflects a synergistic effect of these two types of enzymes.